This invention relates to a method charging of a battery based upon an estimated battery temperature, and, more particularly, to an apparatus estimation of a vehicle's battery temperature under varying conditions. The estimated vehicle temperature is based upon the temperature sensed at one or more temperature sensors disassociated from the battery and a value representative of vehicle speed.
In most vehicles, the vehicle battery is charged using the rectified output voltage from an alternator, wherein the level of voltage at which the battery is charged is controlled by a voltage regulator. Furthermore, it is known that a battery's charging characteristics are dependent upon the temperature of the battery, and, in particular, that there are optimal ranges of charging voltages associated with different battery temperatures. Some of the problems encountered when a battery is charged at voltages poorly suited for the battery temperatures are shortened battery life, and, in some cases, battery damage.
Accordingly, to properly charge a vehicle battery, the voltage at which the battery is charged should be based upon the temperature of the battery. Additionally, when battery temperature is used as a guide for determining the charge voltage of a battery, a method or apparatus must be provided to supply a relatively accurate representation of the battery temperature.
U.S. Pat. Nos. 4,598,373 (Morishita et al., issued on July 1, 1986) and 4,608,639 (Morishita et al., issued on August 26, 1986) recognize the difficulties in effectively correcting for a battery's changing charging characteristics due to temperature changes of the battery.
U.S. Pat. No. 4,598,373 relates to a charge control apparatus for a vehicle having a microcomputer which calculates a battery charging value or voltage regulator set value on the basis of detected engine and charging system parameters. The apparatus includes a microcomputer for providing a reference voltage signal based upon: the charge condition and service life condition of the battery; voltage data; battery terminal data; battery sensor data; charge-discharge current data; and engine data. The reference voltage signal is applied to the external control terminal of the voltage regulator. The voltage at the control terminal is thereby set to a value which is calculated from the various data for suitably charging the battery. In the preferred embodiment of the apparatus, the battery sensor data includes the solution temperature, specific gravity, or acidity of the battery.
U.S. Pat. Nos. 4,608,639 relates to a charge control apparatus having a microcomputer for: processing charging system data such as battery output voltage, generator output voltage, and generator output current; and generating at least one engine parameter from an engine control microcomputer to provide a suitable voltage to charge the battery. In the preferred embodiment of the apparatus, the engine parameters include intake air temperature, engine r.p.m., crank angle, exhaust gas temperature, or air-fuel ratio.
In addition to the problem of determining an optimum voltage at which a battery should be charged for a given temperature, economic and quality control constraints have forced vehicle manufacturers to reduce the number of sensors used in a vehicle where possible. Thus, in some situations, a temperature sensor at the battery for providing actual battery temperature data will not be available. Accordingly, it would be advantageous if the temperature of a vehicle battery could be determined or estimated without requiring a separate temperature sensor at the battery. Rather, it would be advantageous to use the data from a preexisting sensors in a vehicle to estimate battery temperature.
One problem encountered when attempting to estimate battery temperatures based upon temperatures sensed at a temperature sensor disassociated with the battery, is that many modern automobiles have underhood temperatures which are extremely dynamic within a very large temperature range. Factors which attribute to this characteristic of modern automobiles are hotter running engines, low profile and aerodynamic front end styles, electric radiator fans, and more compact underhood designs. For example, the temperature at a voltage regulator is a poor estimate of battery temperature since the voltage regulator has a lower thermal mass than the battery and will have a temperature which follows underhood temperatures much closer than that of the battery.